There are no actual folk clubs in the area of Southern, California where I live. There are some clubs (not called folk clubs)that have open mikes on certain nights but not billed as a folk night or venue. You might hear blues, punk and a little of everything - by mostly amateurs and not necessarily folk at all.

There are house concerts (none in my area) in Southern, Calif. that do book known folk singers - but alas none near me.
The only thing that happens somewhat in my area is folk music get- together (singarounds) at different homes but not always that close to me either.

They are typically singarounds you might say where the chairs are set up in a circle in the living room and everyone can sing a song of their choice (or if there is a particular theme that night - the song will be close to that theme) If you are not a singer or guitar player then you can request a song and hopefully someone there will know it.

I can't sing unfortunately and only know a few chords on the guitar.
Hard for me to even really play guitar anymore because of pain in my right hand (I am right handed)and somewhat on left hand too. So on the rare occasion I might go to one of these get music nights at someone's home, I will just request a song. However, majority of people can sing & play guitar. It is very casual.
They usually are just once a month in different people's houses in various cities in the county I live (large county though)so even at that they are not always that close. You know everything here is so spread out to get places in Southern, California. No subways (in my area) and not much pubic transit buses at night in my area after 8 PM. (especially to residential areas) where these house singarounds are located.

I kind of wish there was a folk club near me that had folk/acoustic music on a regular basis. I just enjoy being a part of an audience with other people and listening to a folk singer on a stage.